The invention relates generally to a method and an arrangement for transferring information in a packet radio service. The invention further concerns the technology of allocating resources for individual radio connections at the interface between a transmitting device and a receiving device, especially the allocation of radio resources for a packet-switched radio connection.
The term xe2x80x9cmobile telecommunications systemxe2x80x9d refers generally to any telecommunications system which enables a wireless communication connection between a mobile station (MS) and the fixed parts of the system when the user of the mobile station is moving within the service area of the system. A typical mobile communications system is a Public Land Mobile Network (PLMN). The majority of mobile telecommunications systems in use at the time of the filing of this patent application belong to the second generation of such systems, a well-known example being the GSM system (Global System for Mobile telecommunications). However, the invention also applies to the next or third generation of mobile telecommunications systems, such as a system known as the UMTS (Universal Mobile Telecommunications System) which currently undergoes standardisation.
Multi-user radio communication systems must have well-defined procedures for allocating radio resources (time, frequency) to individual radio connections. In this patent application we will consider especially packet-switched radio connections in cellular radio systems where each cell comprises a base station which is arranged to communicate with a multitude of mobile stations. As an example we will discuss the well-known GPRS system (General Packet Radio Service), the known resource allocation procedures of which are laid down in the technical specification number GSM 04.60 published by ETSI (European Telecommunications Standards Institute) [1].
Packet switched wireless networks, such as GPRS (General Packet Radio Service), are designed to provide data services, e.g. Internet services, cost-effectively. In GPRS the channels are not dedicated to one user continuously but are shared between multiple users. This facilitates efficient data multiplexing. However, different kind of data services have different requirements for the data connection. For example, Internet real time services have gained popularity during the past few years; IP (Internet Protocol) telephony and different streaming applications are already common in the Internet. These services have different requirements for the data connection compared to, for example, transferring facsimiles or email messages. Therefore the connection for the data transfer is usually established according to the service requirements, such as the Quality of Service (QoS) requirement. This, however, makes the use of many kinds of services during the same connection difficult or impossible.
In order to better understand the problems of the prior art solutions and the idea of the present invention, the structure of a prior art digital cellular radio system is next described in short, and GPRS is then described in more detail by briefly describing some parts of said specification [1].
FIG. 1a shows a version of a prior known GSM cellular radio system. The terminals MS are connected to the radio access network RAN which includes the base stations and the base station controllers/radio network controllers RNC. The core network CN of a cellular radio system comprises mobile services switching centres (MSC) and related transmission systems. If the system supports GPRS services, the core network also comprises Serving GPRS Support Nodes (SGSN) and Gateway GPRS Support nodes (GGSN). According e.g. to the GSM+ specifications developed from GSM the core network may provide new services such as GPRS. The new types of radio access networks can co-operate with different types of fixed core networks CN and especially with the GPRS network of the GSM system.
FIG. 1b shows an architecture of a general packet radio service (GPRS). The GPRS is a new service that is currently based on the GSM system but it is supposed to be generic in the future. GPRS is one of the objects of the standardisation work of the GSM phase 2+ and the UMTS at the ETSI (European Telecommunications Standards Institute). The GPRS operational environment comprises one or more subnetwork service areas, which are interconnected by a GPRS backbone network. A subnetwork comprises a number of packet data service nodes (SN), which in this application will be referred to as serving GPRS support nodes (SGSN) 153, each of which is connected to the mobile telecommunications system (typically to a base station through an interworking unit) in such a way that it can provide a packet service for mobile data terminals 151 via several base stations 152, i.e. cells. The intermediate mobile communication network provides packet-switched data transmission between a support node and mobile data terminals 151. Different subnetworks are in turn connected to an external data network, e.g. to a Public Data Network (PDN) 155, via GPRS gateway support nodes GGSN 154. The GPRS service thus allows the provision of packet data transmission between mobile data terminals and external data networks when the appropriate parts of a mobile telecommunications system function as an access network.
In order to access the GPRS services, a mobile station shall first make its presence known to the network by performing a GPRS attachment. This operation establishes a logical link between the mobile station and the SGSN, and makes the mobile station available for SMS (Short Message Services) 158, 159, over GPRS, paging via SGSN, and notification of incoming GPRS data. More particularly, when the mobile station attaches to the GPRS network, i.e. in a GPRS attachment procedure, the SGSN creates a mobility management context (MM context). Also the authentication of the user is carried out by the SGSN in the GPRS attachment procedure. In order to send and receive GPRS data, the MS shall activate the packet data address wanted to be used, by requesting a PDP activation procedure (Packet Data Protocol). This operation makes the mobile station known in the corresponding GGSN, and interworking with external data networks can commence. More particularly, a PDP context is created in the mobile station and the GGSN and the SGSN. The packet data protocol context defines different data transmission parameters, such as the PDP type (e.g. X.25 or IP), the PDP address (e.g. X.121 address), the quality of service (QoS) and the NSAPI (Network Service Access Point Identifier). The MS activates the PDP context with a specific message, Activate PDP Context Request, in which it gives information on the TLLI, the PDP type, the PDP address, the required QoS and the NSAPI, and optionally the access point name (APN).
FIG. 1b also shows the following GSM functional blocks: Mobile Switching Center (MSC)/Visitor Location Register (VLR) 160, Home Location Register (HLR) 157 and Equipment Identity Register (EIR) 161. The GPRS system is usually also connected to other Public Land Mobile Networks (PLMN) 156.
Functions applying digital data transmission protocols are usually described as a stack according to the OSI (Open Systems Interface) model, where the tasks of the various layers of the stack, as well as data transmission between the layers, are exactly defined. In the GSM system phase 2+, which in this patent application is observed as an example of a digital wireless data transmission system, there are five operational layers defined.
Relations between the protocol layers are illustrated in FIG. 2. The lowest protocol layer between the mobile station MS and the base station subsystem is layer 1 (L1) 200, 201, which corresponds to a physical radio connection. Above it, there is located an entity corresponding to the layers 2 and 3 of a regular OSI model, wherein the lowest layer is a radio link control/media access control (RLC/MAC) layer 202, 203; on top of it a logical link control (LLC) layer 204, 205; and topmost a radio resource control (RRC) layer 206, 207. Between the base station subsystem UTRA BSS of the generic radio access network and an interworking unit/core network IWU/CN located in the core network, there is assumed to be applied a so-called Iu interface, where the layers corresponding to the above described layers from L1 to LLC are the layers L1 and L2 of the OSI model (blocks 208 and 209 in the drawing), and the layer corresponding to the above described RRC layer is the layer L3 of the OSI model (blocks 210 and 211 in the drawing).
The mobile station MS must include a higher-level control protocol 212 and a protocol 213 for serving higher-level applications, of which the former communicates with the RRC layer 206 in order to realise control functions connected to data transmission connections, and the latter communicates directly with the LLC layer 204 in order to transmit such data that directly serves the user (for instance digitally encoded speech). In the mobile station of the GSM system, blocks 212 and 213 are included in the above-mentioned MM layer.
In GPRS, a Temporary Block Flow (TBF) is created for transferring data packets on a packet data channel. The TBF is a physical connection used by two mutually communicating Radio Resource (RR) peer entities to support the unidirectional transfer of Logical Link Control (LLC) Packet Data Units (PDU) from upper Logical Link Control (LLC) layers on physical channels for packet data. We will consider separately uplink TBFs (transfer of data from the mobile station to the base station) and downlink TBFs (transfer of data from the base station to the mobile station).
During an uplink TBF the mobile station will organise the data to be transferred into Protocol Data Units or PDUs. These are in turn divided into smaller parts which are distributed into data blocks on the RLC layer which defines the procedures related to information transfer over the radio interface. Each RLC data block will have a corresponding identification number as well as a multitude of associated fields containing information that relates to the contents and significance of the RLC data block. During a downlink TBF a similar arrangement of successive RLC data blocks is produced by the network and transmitted to the mobile station.
The TBF is thus established using a determined set of parameters for the data transfer, such as acknowledged/unacknowedged RLC mode, radio priority etc. If the mobile station with an existing TBF needs to transfer LLC PDUs with a different RLC mode the existing TBF is released and the new TBF is established for the new RLC mode. This means that the mobile station must request a completely new allocation of radio resources by first transmitting a request message on an access channel (PRACH or RACH; Packet Random Access Channel or Random Access Channel depending on whether or not the first one of these is available). The network will either grant or reject the request by sending a corresponding message on an access grant channel (PAGCH or AGCH; Packet Access Grant Channel or Access Grant Channel, same considerations of availability apply). This procedure of changing the RLC mode may cause an unacceptable delay in the uplink data transfer.
In downlink, to change RLC modes the network must allow for the termination timer in the mobile station to expire for terminating the existing TBF allocation, and establish a completely new TBF by sending a Packet Downlink Assignment message on a PCCCH or CCCH (Packet Common Control Channel or Common Control Channel depending on availability). This procedure may also cause an unacceptable delay in the downlink data transfer.
In the prior art systems it is not possible to transfer simultaneously LLC PDUs using different RLC modes, different radio priorities or different throughput classes. This is a difficult limitation, because in a GPRS system a mobile station may support different types of services and therefore there may also exist a need to transfer LLC PDUs with different parameters simultaneously. Especially, if one of the supported services is a real time service, the delay caused by releasing the existing TBF and the establishment of new TBF to support the service could be unacceptable.
It is thus an object of this invention to provide a method and an arrangement that offers solutions to the prior art problems. Especially, it is an object of this invention to provide a solution for enabling a fluent continuation from a packet-switched service using a first set of communication parameters to second one with a second set of parameters. It is also an object of the invention that it will require only a moderate amount of signalling over the radio interface.
The objects of the invention are fulfilled by providing a procedure, in which at least two simultaneous TBFs can be assigned for a determined transfer direction between a mobile station and the network. Thus a new TBF can be created when data transfer requires a change of communication parameters, and there are no pauses in the data transfer due to release procedures of the existing TBF. It is also possible to use several different types of services simultaneously, because with the present invention it is not necessary first to release the on-going temporary block flow in order to establish a new TBF for transferring LLC Packet Data Units using for example different RLC modes simultaneously, such as transferring IP telephony and Mobility Management messages.
It is thus characteristic to a method according to the present invention for transferring at least one data flow by creating at least one connection between a mobile station and network on a packet radio service of a telecommunication system, said at least one connection constituting a temporary block flow on a packet data channel, that at least two simultaneous temporary block flows are assigned for transferring the at least one data flow during the at least connection.
The invention also applies to a telecommunications system for transferring at least one data flow by creating at least one connection between a mobile station and network on a packet radio service of a telecommunication system, said at least one connection constituting a temporary block flow on a packet data channel, comprising means for assigning for a determined transfer direction at least two simultaneous temporary block flows for transferring the at least one data flow during the at least one connection.
The invention also applies to a mobile station comprising means for transmitting/receiving at least one data flow on at least one connection between the mobile station and network on packet radio service of a telecommunication system, said at least one connection constituting a temporary block flow on a packet data channel, the mobile station comprising means for constituting for a determined transfer direction at least two simultaneous temporary block flows.
Preferred embodiments of the invention are presented in dependent claims.
The inventive procedures used for TBF management support one or several simultaneous TBFs for a determined transfer direction between a mobile station and the network. Each TBF preferably comprises different identifiers (TFI), different RLC parameters used for controlling the transmitting/receiving of data, and separate data buffers. Radio resources for the TBFs are preferably assigned in such a way that the multislot capability of the mobile station is taken into account Radio resources assigned for the temporary block flows comprise one or several channels that may also be partly the same channels or exactly the same channels.
In uplink, if there is no existing TBF between the mobile station and the network in the direction concerned, a TBF can be established in a prior known manner as is described in [1]. If the mobile station has already an existing TBF in uplink, the establishment of further TBF may be preferably requested as follows:
The mobile station may transmit a separate control message, such as a Packet Resource Request message, to the network using the existing radio resources of existing TBF by replacing the sending permission of the existing TBF with the control message. The network will then respond to the mobile station using any existing radio resources, e.g. on the resources of the same TBF on which the network has received the request message.
The mobile station may include the TBF establishment request into a message belonging to an existing TBF when sending the message to the network.
The mobile station may use a signalling or a control channel to request the establishment of a new TBF.
In downlink, if there is no existing TBF between the mobile station and the network in the direction concerned, a TBF can be established in a prior known manner as described in document [1]. In case there is already an existing downlink TBF between the mobile station and the network, an establishment of a further TBF may be accomplished preferably in one of the following ways:
The network may send a separate control message, such as a Packet downlink Assignment, to the mobile station using the existing radio resources of another TBF by replacing the sending permission of the other TBF with the control message.
The network may include network establishment request into a message that belongs to another TBF when sending the message to the mobile station.
The network may also use a signalling channel or a control channel to notify the mobile station of the establishment of a new TBF.
The temporary block flows are scheduled independently, i.e. the transmission and receiving permissions are assigned independently. However, the multislot capability of the mobile station is preferably taken into account. The multislot capability means that the mobile station is able to transmit more than one channel and/or receive more than one channel within the TDMA frame. When using the multislot capability of the mobile station the network should also take into account that the mobile station may require time gaps in order to perform channel and neighbouring cell measurements. The network has the information about the other existing TBF(s) of the mobile station, so the network is able to take the requirements of the mobile station into account. Otherwise, the transfer of data may follow the prior art procedures that are described in [1].
The mobile station may get individual identifiers for each TBF. This way the network is able to priorise transmissions of different connections by giving a transmission permission for a determined TBF. Another alternative is that mobile station gets an identifier for all TBFs in a determined transfer direction (uplink/downlink). In this case, for example in uplink data transfer the network gives transmission permissions for the mobile station and the mobile station may decide which one of the uplink TBFs gets the transmission turn. This way the network can not priorise the traffic efficiently.
The release of each TBF can be made independently by, e.g. following the prior art procedures described in [1]. Alternatively the mobile station may inform the network with a message/parameter that it wishes to release all the TBF(s) in the certain transfer direction or that it wishes to release all the TBF(s) in the both transfer directions (uplink and downlink). An advantage of this procedure is that resources are saved, as only one message/parameter is required for releasing many TBFs instead of one message/parameter for each released TBF.